The invention concerns a procedure for the determination of the length of a standard code sequence of a CDMA (Code Division Multiple Access) signal. In the case of the standard code sequence, the involved matter is a standardized code sequence transmitted in a defined code channel. The standard code sequence can, for example, be placed before the data to be transmitted, thus being the “preamble”, or also in the middle of the transmitted data, thus becoming the “midamble”.
CDMA signals encompass a plurality of code channels, which, channels respectively, are separated by different, orthogonal, spread-codes, and are simultaneously transmitted. After the separation a scrambling is effected with a scrambling code. The present invention is employed for the detection of the preamble length of a CDMA signal from the base stations of the 1×EV-DO Mobile Radio systems. This standard is described in detail by the document 3GPP2, Cdma2000 High Rate Packet Data Air Interface Specification (3GPP2, C. S0024) Chapter 9.3 of Aug. 23, 2001).
The CDMA signal in accord with the above signal, is special in that the data sequence precedes a standard code sequence as a preamble, which can have chips of different lengths, namely, 1024, 512, 256, 128, or 64. It can also occur, that no standard code sequence (preamble) is transmitted. Although, in the transmitting of the standard code sequence (preamble) a code channel of the code class CCpreamble=5, is employed, with a spreading factor SF=25, then, for the transmission of the data, all code channels of the code class CCdata=4, are used and in this case, also with a spreading factor SF=24. For the transmission of the standard code sequence (preamble), besides this, only one code channel is active, whereby, as a rule, it is not known which code channel is involved with which code number CN. The code channel with the number CN=0 is, however, always inactive. For a scenario of a CDMA signal of this type, the necessity arises, of detecting, for instance with a measuring instrument, the length of the standard code sequence (preamble). The length of the standard code sequence (preamble) is not known, and runs, for instance 1024, 512, 256, 128, or 64 chips.
Since cases can be found, in which no standard code sequence (preamble) is transmitted, the determination must be made, as to whether or not indeed any standard code sequence was sent. As to the state of the technology, one may refer to DE 199 53 349 A1. This publication discloses a procedure for the synchronization of a CDMA received signal. A detection of the standard code sequence (preamble), however, is not carried out.
Thus the invention has the purpose of creating a procedure for the determination of the length of a standard code sequence of a CDMA signal and also to create a corresponding computer program, which incorporates a minimum of numerical complexity and can be implemented with small effort, that is, has a short computation time.